Disc storage media such as CDs (Compact Discs), DVDs (Digital Versatile Discs), and BDs (Blu-ray Discs) allow random access in which direct access to a position of intended data is allowed.
However, an access time required for random access varies depending on devices. In particular, an optical disc drive device for reading and writing information from/onto an optical disc is slower in access speed than magnetic disk devices such as hard disk drives.
Recent years, an operating system (OS) environment of a computer is often shared between different computers. That is, different computers often operate in a same OS environment. In such a case, a user has to take out a medium storing OS data from a device so as to carry the medium from one computer to another. Therefore, the user runs the OS by use of an optical disc drive device from which the medium can be taken out. However, as described above, optical disc drive devices have a shortcoming in that access speeds are slower than hard disk drives.
An access time is determined by a seek time which is a time until a head is moved to a predetermined position on a disc or by a rotational latency of the disc which is a time until a predetermined sector is read by the head. Therefore, in order to reduce the access time, it is necessary to reduce the seek time by improving an actuator or to reduce the rotational latency by increasing the number of rotations of the disc. However, such improvement of an optical disc drive device is nearly reaching limitation of reduction of an access time. Therefore, different measures are sought after for further reduction of an access time.
Patent Literature 1 discloses a magnetic disk device which has a nonvolatile memory so as to allow reduction in access time. Specifically, in the magnetic disk device disclosed in Patent Literature 1, logical addresses are assigned to the nonvolatile memory so that the nonvolatile memory can be handled as logical sectors on a magnetic disk. Thus, the magnetic disk device handles the magnetic disk and the nonvolatile memory as one virtual storage medium. This allows a higher access speed in the case of reading and/or writing of data stored in the nonvolatile memory, as compared to reading and/or writing of data from/onto the magnetic disk.
Citation List
Patent Literature 1
Japanese Patent Application Publication, Tokukaihei, No. 06-314177 A (Publication Date: Nov. 8, 1994)